1. Field of the Invention
The present invention relates to a method and structure for connecting two plastic pipes to each other in a T-shaped form through electric fusion.
2. Description of the Related Art
Electric fusion is generally used to connect pipes to each other, and connection of pipes will be described below centered on such electric fusion.
In bonding of pipes made of polyethylene, polypropylene or the like to be used for gas pipes, tap water pipes and other purposes, heat fusion methods have been mainly used to provide a completely hermetic seal.
Conventional heat fusion methods are classified into a butt fusion method, a heat fusion socket method, an electro-fusion socket method, an electric fusion method, and so on.
Butt fusion is also referred to as butt fusion welding, in which ends of pipes are butted and fused to each other without use of a separate socket. In detail, butt fusion is conducted according to the following steps of: fixing the pipes in hydraulic or pneumatic clamps in such a way that the ends of the pipes to be fusion-bonded face each other; smoothing the ends of the pipes to be fusion-bonded; placing a heating plate between the ends of the pipes; tightly pressing the ends of the pipes onto the heating plate using hydraulic or pneumatic pressure; heating the heating plate to an appropriate melting point (e.g., about 210° C. for polyethylene) to fuse the ends of the pipes; rapidly removing the heating plate from the pipes; tightly pressing the fused ends of the pipes onto each other; and cooling the pipes while maintaining them in the above state for a predetermined time until the fused ends of the pipes are solidified, thus completing bonding of the pipes.
The above-mentioned method bonds the pipes by melting pipe materials and does not require use of a separate socket. However, this method requires a heat welding machine which is heavy to carry to a working site and has a complex structure.
Another method uses a typical connection socket, in which the inner circumferential surface of the socket and the outer circumferential surfaces of pipes are melted at the same time and then bonded together. That is, the outer circumferential surfaces of the pipes and the inner circumferential surface of the socket are heated at the same time so that the target surfaces are fused simultaneously, and after they are heated sufficiently, the inner circumferential surface of the socket is rapidly fitted over the outer circumferential surfaces of the pipes. Thereafter, the coupled pipe structure is cooled for a predetermined time.
Hereinafter, the electro-fusion socket method will be explained. This process uses a socket which has therein a heating element such as a heating coil. The socket is injection-molded with the heating element integrally disposed therein. For example, a copper wire, a copper alloy wire, a nichrome wire, etc. which have an appropriate degree of electrical resistance is used as the heating coil. Such an electro-fusion socket integrally provided with an electric resistance wire is manufactured by winding an electric resistance wire coated with thermoplastic resin in a coil form, connecting electric terminals to ends of the wire, disposing the wire in a mold, and molding resin. After the socket manufactured in this way is fitted over pipes to be fused, electric current is applied to the socket for a predetermined time by a simple power supply. Then, the outer circumferential surfaces of the pipes and the inner circumferential surface of the socket are fused at the same time and bonded together.
Such an electro-fusion socket method is also referred to as electric fusion or electro-fusion.
Electric fusion has been generally used for seamed pipes.
At present, electro-fusion seamed pipes are preferred by users because of facilitation of work, and various heating elements for the electro-fusion connector pipes are being developed.
In addition to the foregoing techniques, incorporated hereby by reference in their entirety into this specification, electro-fusion techniques were also proposed in Korean Patent Laid-open Publication No. 10-2002-0012809, entitled “ELECTRONIC FUSION SHEET OF THERMOPLASTIC (E.G., POLYETHYLENE OR POLYPROPYLENE) PIPES USING PRINTED (COATED) HEATING CIRCUIT,” Korean Patent Laid-open Publication No. 10-2004-069622, entitled “HEAT GENERATING BUSHING FOR FUSION OF PLASTIC PIPES,” Korean Patent Laid-open Publication No. 10-2004-0096757, entitled “FUSION STRUCTURE FOR PLASTIC PIPES,” Korean Patent Laid-open Publication No. 10-2005-0003231, entitled “FUSION STRUCTURE FOR PLASTIC PIPES USING FUSION RING” and so on.
Meanwhile, another conventional technique was proposed in PCT International Application No. PCT/KR2007/000540, entitled “ELECTRIC FUSION PIPING MATERIAL WITH SCREW PRESSING DEVICE”, which was filed by the applicant of the present invention. This conventional technique provides an electric fusion piping device which includes a pipe joint made of plastics to be connected with a plastic pipe. The pipe joint has a thread formed on an inner circumferential surface thereof for threaded coupling. An annular heating element is provided in an inner circumferential surface of the pipe joint for electric fusion. The electric fusion piping device further includes a pressing member. The pressing member includes a threaded portion which engages with the thread of the pipe joint, and a pressing portion which moves forward in response to rotation of the threaded portion to press the annular heating element. Particularly, in this technique, conductive plastic is used as the material of the annular heating element.
Such processes of connecting plastic pipes are mainly conducted in such a way that linear pipes are arranged in a line and then connected to each other.
Meanwhile, a plastic pipe may be connected at an end thereof to another plastic pipe that has been installed, after a connection hole is formed the existing plastic pipe. In other words, a plastic pipe may be required to be connected to the existing plastic pipe in a branch form on a construction site.
In this case, typically, butt fusion method or heat fusion socket method is mainly used.